Someone who won't give up anything under interrogation.
Standing up to questioning.

Cop: Awright asshole, where'd you get that illegal substance?
Guy: I dunno what that is or how it got there. Never seen it before.
Cop: Oh yeah? We're gonna lock up up and throw away the key if you don't tell us where you got that stuff.
Guy: I don't know NOTHIN' about it!